The present invention relates to an electrical waveform synthesizer, and more particularly, to a synthesizer utilizing a shift register and a digital-to-analog converter for generating an acoustic waveform. Additionally, the present invention relates to a fine frequency vernier for providing a finely adjustable clock frequency to the shift register.
There are many requirements for an acoustic signal source which is compact, economical, and computer controlled for providing signal generating capability for a variety of requirements. Additionally, it is desirable that the acoustic signal source be able to simulate a plurality of acoustical environments, such as, to simultaneously generate a plurality of sine waves each with an assignable frequency and range of amplitudes to represent the acoustic signature such as an antisubmarine warfare (ASW) threat, apply a frequency vernier for simulating Doppler effects, individually control sine wave amplitudes to give the effect of tonal source strength dependence, vary the signal strength to represent detection response due to circle spreading and bottom bounce, and provide appropriate signals for testing a receiver sensitive to the synthesized acoustic waveforms. Additionally, it is desirable that any changes in signal output would cause a minimum of transients, and that unintentional harmonics should be attenuated at least forty dB.